Method for making products from powdered materials

ABSTRACT

The invention relates to the powder metallurgy. The invention involves deforming combustion products by extrusion at an extrusion temperature chosen in the range from 0.3T 1  to T 2 , wherein T 1  is the melting point of a hard phase of the combustion products and T 2  is the melting point of a binder material in a container (5) made up of vertically extending segments (12) defining spaces (13) with one another and having a die (14) and a heat insulated sizing member (17) the temperature conditions of extrusion being controlled by means of a unit (21) having a temperature pick-up (22) and a member (23) receiving information from the pick-up (22) and sending a command for moving the punch (10).

TECHNICAL FIELD

The invention relates to the powder metallurgy and, in particular, itdeals with a method and apparatus for making products from powderedmaterials.

BACKGROUND OF THE INVENTION

Known in the art is a method for making products from powderedheat-resistant materials by hot impact extrusion, comprising preparingcylindrical compacts by using conventional techniques of powdermetallurgy, hydrostatic pressing of compacts under a pressure of 150 to460 MN/m², sintering them in vacuum at up to 1450° C. during 1 to 6hours, and subjecting the compacts to hot dynamic extrusion with glasslubricant, with subsequent annealing in vacuum during one hour (Abstr.Jr. "Metallurgia", 1981, 1Γ445; City of London Polytechnic, Dep. ofMetallurgy and Materials. Ill. 12; Table ; ref. 9. "Hot Impact Extrusionand Subsequent Treatment of Some High-Temperature Nickel Alloys"). Thedynamic extrusion allows high-temperature nickel-based alloys containingless than 50% of a high-melting component to be processed, and incertain applications it is capable of hot hardness, lowering porosityand distribution of particles in the material.

The main disadvantages of this method are due to its multiple-stageimplementation which results in a substantial energy consumption, theneed to use sophisticated production equipment, long process time andhigh labour effort. In addition, it is known that sophisticated alloyscontaining more than 50% of a high-melting component are not suitablefor dynamic extrusion because of high hot and hardness.

Known in the art is a method for making products from hard alloycomposite comprising carrying out a combustion reaction in a mixture ofstarting powders (metal, nonmetal and binder), with subsequentdeformation of the mixture by three-dimensional compression ("NewMethods for Making High-Temperature Materials Based on Combustion".Merzhanov A. G., Borovinskaya I. P., Yukhvid V. I., Ratnikov V. I. inthe book "Scientific Fundamentals of Materials Technology" (in Russian).Moscow, Nauka Publishing House, 1981. pp. 193-206). This method can beregarded as a modification of hot pressing in which the combustionprocess prepares components for deformation of the material synthesisand heating). This method was used for making a tungsten-free hard alloyfrom elements (Ti, C, Ni, Mo). The mixture is blended for obtainingindustrial alloys (titanium carbide with 20 and 30% of nickel andmolybdenum binder). Materials with rather good properties close tocommercially applicable grades can be produced under certain conditions.The method of self-propagating high-temperature synthesis undercompression is used nowadays also for producing compact material fromindividual high-melting compounds.

The abovementioned method makes it possible to produce hard-alloymaterials and products in a single stage during a short time period(about one munite) with minimum energy consumption.

The main disadvantage of the method is the limitation of configurationof products so that elongated products, i.e. products having a largelength-to-diameter ratio (h/d>>1) are produced. The non-uniformthree-dimensional compression pattern used in this method results inmainly compressive stresses being built up in the material. For thisreason, if products with h/d>1 are made by this method, they loose theinitial shape with fracturing and underpressing.

Known in the art is a method of self-combustion sintering of ceramicsunder pressure, comprising propagation of exothermal synthesis reactionunder a high pressure, wherein the synthesis and compaction of thesintered material are carried out in a blended powdery mixturecontaining elements necessary for the synthesis (Miyamoto K., Kamija H.,Koizumi M. "High-Pressure Self-Combustion Sintering of Ceramics." Funtaioyobi Funmatsu Jaken. 1987, vol. 34. No. 3. pp. 101-196 (JP) CA 107No 1. p. 266 (119811H). Abstr Jr. Khimia 1988, vol. 13, p. 11, 7E, 13M).

In this method, heat released as a result of the synthesis reaction isthe source of energy for sintering under pressure. A thermal impulseshould be applied to the mixture to initiate the process (by causing acurrent of 200-400A to flow during 3 seconds) whereafter the processoccurs very rapidly (for about several seconds). High-melting materialssuch as TiB₂, ZrB₂, NbB₂, TiC, SiC as well as composition materials andproducts on their base can be manufactured using this simultaneoussynthesis and sintering.

Known in the art is an apparatus for carrying out this method comprisinga reactor in which is placed into a high-pressure chamber. The reactoris in the form of a hexahedron of pyrophillite having boron nitrideliners in which a starting mixture is charged. The mixture is ignited atone point or at the entire side surface thereof.

Advantages of the above described method and apparatus reside in a shortprocess time and low power requirements. Disadvantage include equipmentdifficulties (an individual reactor is necessary for each size and shapeof product), low productivity because the reactor should be placed inthe high-pressure chamber, and product size limitation which is alsoimposed by the construction of the apparatus.

The most similar to the invention is a method for making products frompowdered materials selected from the group consisting of at least onetransition metal, at least one nonmetal, and at least one metal-basedbinder material, comprising preparing a powdery mixture of saidmaterials, initiating a combustion reaction therein with the formationof a solid phase from said transition metal and nonmetal in thecombustion products, with subsequent deformation of the combustionproducts and removal of the finished product.

Known in the art is an apparatus for carrying out this method,comprising a mold having a container for a powdery mixture, a device forinitiating a combustion reaction in the mixture in the container, apunch for deforming the combustion products in the container, and apress for developing pressure for deforming the combustion productshaving a ram operatively connected to the punch and ram movement controlsystem (Richardson G. Y., Rice R. W., McDonough W. J., Kunet J. M.,Schroeter T. "Hot Pressing of Ceramics Using Self-PropagatingSynthesis". Ceram. Eng. Sci. Proc. 1986, vol. 7, No. 7-8, pp. 761-770.Abstr. Jr. "Khimia., M., 1987, No. 4, 4II20).

In accordance with this method, the starting mixture is briquetted andplaced into the apparatus.

The apparatus for carrying out the method comprises a graphite mold witha punch and a container lined with a layer of a fibrous ceramicinsulation 1.5 cm thick. This facility makes it possible to carry outthe induction heating of the mold to a high temperature (1000° C.).Before initiation of the combustion reaction, a pressure of 34 MPa isapplied to the briquet in the mold. The device for initiating thecombustion reaction in the mixture is located outside the moldcontainer, and a combustion wave propagates through the powdery mixturecontained in a passage of the mold base, up to the briquet. After theignition of the reagents the pressure materially drops (to about 50% ofthe initial value), and the pressure is then again raised to 34 MPaduring about two seconds and is kept at this level during 5 to 10minutes. The material is compacted by a hot forming press having acontrol system.

This method was used to make TiC-based materials containing 10-30 vol. %of Ti as binder and also TiC-TiB₂ -based materials.

The above-described method and apparatus cannot be used for makingelongated products (with a height-to-diameter ratio much greater thanunity) because of the axial pressing resulting in compressive stressesonly being built up in the material. Samples produced in the abovedescribed apparatus are in the form of discs 2.8 cm in diameter and 0.3cm thick. Attempts to obtain products with h/d>>1 with such a loadingpattern ended in fracturing of the sample and underpressing of certainportions.

In addition, there is no control of temperature of the material, whichmay result in non-uniformity of structure and composition of thematerial over the volume of the product. This inhomogeneity generallyoccurs in deforming materials in which components are in differentstates, e.g. the hard base is in the solid state and the metal binder isin the liquid state.

SUMMARY OF THE INVENTION

The main object of the invention resides in providing a method formaking products from powdered materials and an apparatus for realizationthereof wherein the products of combustion would be so deformed as tomake compact long-measure products (h/d>>1) with homogeneous structureand composition throughout their volume.

This object is accomplished by a method for making products frompowdered materials selected from the group consisting of at least onetransition metal, at least one nonmetal, and at least one metal-basedbinder material, comprising preparing a powdery mixture of saidmaterials, initiating a combustion reaction therein with the formationof a solid phase from said transition metal and nonmetal in thecombustion products, with subsequent deformation of the combustionproducts and removal of the finished product; according to theinvention, the combustion products are deformed by extrusion at anextrusion temperature of the combustion products ranging from 0.3T₁ toT₂, wherein T₁ is the melting point of the solid phase of the combustionproducts and T₂ is the melting point of the binder and under a pressureP ranging from 2000 to 5000 kg/cm².

When the combustion products are exposed to a temperature ranging fromthe combustion temperature to the melting point of the binder material,processes of formation of a crystalline structure from completelyreacted materials of the starting mixture have time to occur, andimpurity gases available in the mixture are removed. The latter resultsin a lower porosity and lower requirements imposed on purity ofmaterials of the starting mixture. Carrying out extrusion of thecombustion products after the solidification of the binder materialensures homogenity of structure and composition lengthwise of theproduct.

The temperature range of the extrusion process is determined inaccordance with the following specific requirements:

of the cure is carried out to a temperature T<0.3T₁, deformation of thecombustion products will occur in accordance with dry friction laws(crystallographic dislocation) which calls for substantial mechanicalforces; temperature gradients are high, and relaxation of thermoelasticstresses occurs mainly through fracturing;

if the cure is carried out to a temperature T>T₂, thermal processesafter the passage of the combustion wave will not have time to form acrystalline structure. As the binder material available in the startingmixture is in the molten state at the combustion temperature, this willcontribute to its spread in the structural framework of the hard phaseof the combustion products and to a uniform distribution of the binderin both longitudinal and transverse directions. However, if theextrusion begins with T>T₂, non-uniform three-dimensional redistributionof the binder lengthwise of a sample occurs owing to strong differencesbetween mobilities of the molten binder material and hard phase.

Therefore, the abovementioned temperature range (0.3T₁ -T₂) of theextrusion process ensures the retention of plastic properties of thehard phase of the combustion products. Carrying out extrusion at atemperature T<0.3T₁ results in a loss of plastic properties of the hardphase. Carrying out extrusion at a temperature T>T₂ cannot provideconditions for uniform distribution of the binder material between hardphase grains.

This object is also accomplished by an apparatus for making productsfrom powdered materials, comprising a mold having a container with aninterior space for a powdery mixture, a device for initiating acombustion reaction in the mixture in the interior space of thecontainer, a punch for deforming the combustion products in the interiorspace of the container, and a press for developing pressure fordeforming the combustion products having a ram operatively connected tothe punch and a ram movement control system, according to the invention,the container is made up of vertically extending segments definingspaces with one another for removing gases from the apparatus, and a diewith an orifice, having a conical entry portion conjugated with the dieorifice and with the interior space of the container and a heatinsulated sizing member for imparting a form to the product areprovided, the cross-sectional configuration of the sizing membercorresponding to the configuration of the die orifice, the ram movementcontrol system having a unit for controlling temperature conditions ofextrusion comprising a temperature pick-up provided on the surface ofthe conical entry portion of the die and a member electrically coupledto the pick-up and press for sending a command for moving the punch.

The combination of the abovementioned structural elements of theapparatus ensures the implementation of the energy-saving method formaking elongated products from powedred materials by combining thecombustion reaction in an exothermal mixture of starting components andsubsequent extrusion of the combustion products with utilization of heatof this reaction.

The provision of the die having the conical entry portion and theheat-insulated guide sizing member having its orifice which is identicalto the die orifice makes it possible to obtain elongated products ofpreset cross-sectional configurations with a high length-to-diameterratio without buckling and fractures.

The construction of the container made up of vertically extendingsegments contributes to the most efficient removal of impurity gasesreleased during combustion along the whole height of the blank throughthe spaces between the segments. Complete degassing can thus be ensuredby the beginning of extrusion so that a compact part can be producedwithout shells and large pores.

In addition, this construction of the container ensures its highresistance to cyclic thermal loads which is very important as acombustion temperature of the mixture is as high as 1500°-3000° C.

The provision of the unit for controlling temperature conditions ofextrusion in the press control system allows high-quality products to bemade in the apparatus with homogeneous structure and composition overproduct volume. This is due to the fact that the temperature pick-upprovided on the conical surface of the die senses the materialtemperature in the zone of maximum heat removal, and the memberobtaining information from the pick-up is adjusted to a preset extrusiontemperature in the range from 0.3T₁ to T₂ and sends a command for movingthe punch when this temperature is reached.

The device for initiating the combustion reaction is preferably providedinside the punch. This simplifies construction of the apparatus andfacilitates the process as there are no obstacles during extrusion ofthe material through the die orifice, and preparation for the next cycleis only reduced to the replacement of a tungsten filament.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to a specificembodiment illustrated in the accompanying drawings, in which:

FIG. 1 shows a general diagrammatic view of an apparatus for makingproducts from powdered materials;

FIG. 2 is a diagrammatic view, in longitudinal section, of an extrusionmold;

FIG. 3 is a sectional view taken along line III--III in FIG. 2.

Best Mode for Carrying Out the Invention

A method for making products from powdered materials according to theinvention is carried out in the following manner. Starting powderscomprise at least one transition metal of groups IV,V,VI of the periodictable of the chemical elements, at least one nonmetal selected from thegroup consisting of C,B,Si,S,Se, and at least one binder based on ametal of groups IV,V,VI of the periodic table of the chemical elementsas well as Fe, Co, Ni, Cu.

Batches of the abovementioned powders are placed in a ball mill andblended using conventional techniques.

The blended powdery mixture is deformed into compacts in a steel moldused for compaction. The compacts are then withdrawn from the mold andheat insulated with asbestos fabric. The compacts are then placed into amold for extrusion, and a combustion reaction is initiated in themixture by causing current to flow through a tungsten filament, theresultant material being cured after completion of the reaction.

During the cure, degassing of the combustion products and formation oftheir crystalline structure occur. When the material temperature dropsfrom the combustion temperature to the extrusion temperature determinedby the formula T=0.3T₁ +T₂, wherein T is the temperature of extrusion ofthe combustion products, T₁ is the melting point of the hard phase ofthe combustion products, and T₂ is the melting point of the bindermaterial, a pressure P ranging from 2000 to 5000 kg/cm² is applied, andthe combustion products are extruded through the die. After cooling ofthe finished product to room temperature it is removed from the mould.

The method is carried out in an apparatus for making products frompowdered materials according to the invention, which comprises a press 1(FIG. 1) for developing pressure for deforming the combustion products,which has a ram 2 and a system 3 for controlling movement of the ram 2,an extrusion mold 4 having a container 5 (FIG. 2) which has an interiorspace 6 (FIG. 3) for a powdery mixture. The apparatus also has a device7 (FIG. 2) for initiating a reaction of combustion in the mixture in theinterior space 6 of the container 5, which has a tungsten filament 8 andleads 9, and a punch 10 having a hole 11 for deforming the combustionproducts in the interior 6 of the container 5 operatively connected tothe ram 2 of the press 1.

According to the invention, the container 5 is made up of verticallyextending segments 12 (FIG. 3) with spaces 13 defined between them forthe removal of gases from the apparatus. The container 5 has a die 14(FIG. 2) having an orifice 15 and a conical entry portion 16 conjugatedwith the orifice 15 of the die 14 and with the interior space 6 of thecontainer 5. The container 5 also has a heat insulated sizing member 17for imparting a form to products which has a cross-sectionalconfiguration corresponding to the configuration of the orifice 15 ofthe die 14. The sizing member 17 is lined with a heat insulator 18 andis located in a bed 19 of the press 1.

The orifice 15 of the die 14 is closed by a plug 20.

The system 3 for controlling movement of the ram 2 comprises a unit 21(FIG. 1) for controlling temperature conditions of extrusion having atemperature pick-up 22 (FIG. 2) provided on the surface of the conicalentry portion 16 of the die 14 and a member 23 receiving informationfrom the pick-up 22 and sending a command for moving the punch 10. Themember 23 is made in the form of an electronic device which iselectrically coupled to the pick-up 22 and to the press 1.

A compact 24 of a powdery mixture is located in the interior space 6 ofthe container 5 and is heat insulated from the walls of the container 5by means of asbestos fabric 25 and from the punch 10 by means of apressure washer 26.

The device 7 for initiating the combustion reaction in the mixture isprovided in the hole 11 of the punch 10.

The apparatus for making products from powdered materials functions inthe following manner. First the compact 24 is molded from a powderymixture containing at least one transition metal of groups IV,V,VI ofthe periodic table of the chemical elements, at least one nonmetalselected from the group consisting of C,B,Si,S,Se, and at least onebinder material based on a metal of groups IV,V,VI of the periodic tableof the chemical elements and Fe, Co, Ni, Cu.

The compact is covered after molding with a heat insulation in the formof the asbestos fabric 25 on the periphery and placed into the interiorspace 6 of the container 5. The tungsten filament 8 is inserted into thedevice 7 for initiating combustion through holes of the pressure washer26. The punch 10 operatively connected to the ram 2 of the press 1 islowered until the filament 8 comes in contact with the compact 24. Thenthe control system 3 electrically coupled to the initiating device 7 andto the unit 21 for controlling temperature conditions of extrusion isswitched on. The control system 3 sends a command to apply to theinitiating device 7 a voltage of 20 to 50 V during 0.5-2 so that thetungsten filament 8 is heated to initiate the combustion reaction in thecompact 24 of the starting mixture. Impurity gases released duringcombustion are removed through the spaces 13 between the segments 12 ofthe container 5 along the whole height of the compact 24.

The temperature pick-up 22 in the form of a tungsten-rheniumthermocouple provided on the surface of the conical entry portion 16 ofthe die 14 records the end of combustion of the compact 24. A signalfrom the temperature pick-up 22 goes to the member 23 in the form of anelectronic device which sends a command for moving the ram 2 and thepunch 10 eperatively connected thereto when the preset temperature isreached. The temperature to which the member 23 is preadjusted is chosenin the range from 0.3T₁ to T₂, wherein T₁ is the melting point of thehard phase of the combustion products, T₂ is the melting point of thebinder material.

The press 1 builds up a pressure of 2000 to 5000 kg/cm² in the tool 4 bymeans of the punch 10.

When a pressure necessary for the deformation of the material of theplug 20 is built up, the plug is forced through, and extrusion of thematerial is started through the orifice 15 of the die 14 into the sizingmember 17. When a preset pressure in the abovementioned range isreached, the control system 3 sends a command for lifting the ram 2 ofthe press 1, and the ram moves back to the initial position. The productis removed from the mold 4 after cooling.

The method and apparatus according to the invention may be illustratedby examples of manufacture of bars 8 mm in diameter from variousmaterials.

EXAMPLE 1

Titanium, carbon and nickel powders were used in the followingproportioning in % by mass: Ti-56; C-14; Ni-30. The powders were blendedin a ball mill, the resultant mixture was molded into 50 g compacts 25mm in diameter, heat insulated with asbestos fabric 1.5 mm thick andplaced into an extrusion mold having the interior space of the container30 mm in diameter and 8 mm-diameter die orifice. The temperature pick-up(tungsten-rhenium thermocouple) was provided on the surface of theconical entry portion of the die. The tungsten filament was insertedinto the electric leads of the initiating device incorporated in thepunch. The punch with the initiating device was lowered into theinterior of the container until the tungsten filament came in touch withthe compact. Voltage of 50 V was applied to the tungsten filament forone second to initiate the combustion reaction in the mixture. Thecombustion temperature of the mixture was 2000° C. As a result ofreaction a TiC-Ni composite was formed. The melting point of the hardphase (TiC) was T.sub. 1 =3200° C. and the melting point of the bindermaterial (Ni) was T₂ =1456° C. The temperature of the synthesizedmaterial was continually recorded by the temperature pick-up. After thepassage of the combustion wave, the material was cured at a presettemperature which was up to 1400° C. (T=0.44 T₁) in this case. When thepreset temperature was reached, the member receiving information fromthe pick-up sent a command for moving the press ram and the punchoperatively connected thereto. The punch built up pressure of 5000kg/cm² in the interior of the container. The synthesized material wasthus compacted and then extruded through the die orifice into the heatinsulated sizing member.

After cooling, the finished product in the form of 8 mm-bar 120 mm longwith an even and smooth surface was removed.

The bar had a defect layer of 0.1 mm per diameter. Investigation intothe quantitative phase composition at various points of the bar gave thefollowing results in % by mass:

leading portion: TiC-70; Ni-30;

trailing portion: TiC-70; Ni-30.

The data for other examples are given in the Table below.

                  TABLE                                                           ______________________________________                                                               Mixture                                                      Composition of starting                                                                        combustion                                                                              Temperature of                               Ex-   mixture, % by mass                                                                             tempera-  the hard phase,                              ample Ti     C      Ni  B    Co  ture °C.                                                                       °C. (T.sub.1)                 ______________________________________                                        1     56     14     30  --   --  2000    3200 (TiC)                           2     56     14     30  --   --  2000    3200 (TiC)                           3     56     14     30  --   --  2000    3200 (TiC)                           4     58.7   6.4    --  14.9 20  2500    2500 (eutec-                                                                  tic TiC + TiB.sub.2)                 5     84     16     --  --   --  2200    3200 (TiC)                           ______________________________________                                                                               Deviation                                    Temperature                 De-  of phase                                     of the bin-           Pro-  fect content                                      der materi-                                                                              Extrusion  duct  lay- lengthwise                             Ex-   al, °C.                                                                           temperature                                                                              length,                                                                             er,  of the pro-                            ample (T.sub.2)  °C. (T)                                                                           mm    mm   duct, %                                ______________________________________                                        1     1456 (Ni)  1400 (0.44T.sub.1)                                                                       110   0.1  0                                      2     1456 (Ni)  1200 (0.38T.sub.1)                                                                       106   0.1  0                                      3     1456 (Ni)  1000 (0.31T.sub.1)                                                                       102   0.1  0                                      4      1490 (Co) 1000 (0.40T.sub.1)                                                                       100   0.1  0                                      5     1680 (Ti)  1500 (0.47T.sub.1)                                                                       115   0.1  0                                      ______________________________________                                    

The method and apparatus according to the invention make it possible toobtain a large range of products with various cross-sectionalconfigurations and with unlimited height-to-diameter ratios.

Products obtained by this method feature homogeneous structure andcomposition over the whole volume and high surface finish; they requirebut a minimum machining.

INDUSTRIAL APPLICABILITY

The invention may be most advantageously used for making elongatedround-section products from high-melting inorganic powdered materials,e.g. punch rolls, tool stems and the like.

The invention may also be used for producing shaped products of variouscross-sectional configurations.

What is claimed is:
 1. A method for making products from powdered materials selected from a group consisting of at least one transition metal, at least one non-metal and at least one binder based on a metal from the periodic table, comprising preparation of a powder-like mixture from said materials, initiation of combustion reaction therein with formation of a hard phase in the combustion products from said transition metal and non-metal followed by deformation of combustion products and extraction of the finished product and wherein the combustion products are deformed by extrusion at an extrusion temperature T of the combustion products from 0.3 T₁ to T₂ where T₁ is the melting point of the hard phase of the combustion products and T₂ is the melting point of the binder material and at a pressure P ranging from 2000 to 5000 kgf/cm². 